President Trump declared war on the conservatives of the House Freedom Caucus on Thursday, suggesting Republicans should “fight them” in the 2018 midterm elections if they do not back his agenda.

“The Freedom Caucus will hurt the entire Republican agenda if they don’t get on the team, & fast,” Mr. Trump said Thursday morning on Twitter, escalating a fight that began when the conservatives from the caucus blocked his Affordable Care Act repeal last Friday.